In general, spray drying may be performed in many ways, and to all varieties it applies that the air distribution in the spray drying apparatus is one of the most vital parts. There are various systems depending on the plant design and the type of product to be produced. Different designs or adjustment of air dispersers are used in spray dryers to achieve either roughly a straight “plug-flow” air stream or a swirling air stream. The most common is that the air disperser is situated on top of the spray dryer ceiling, and the atomizing device(s) is/are placed at the middle of the air disperser thus ensuring an optimal mixing of the air and the atomized droplets.
The set of guide vanes is arranged in a guide vane framework to provide the distribution of drying air inside of the air disperser. Examples of prior art air dispersers incorporating such a framework are U.S. Pat. No. 4,227,896 (Niro) and WO 2007/071238 A1 (Niro).
In the latter document, the air disperser comprises a plurality of guide vanes positioned substantially vertically in the axial direction and substantially on the radii in a space defined by the pipe wall and the outer wall of the air disperser, and at least one of the guide vanes is covering at least 90% of the full radius from the pipe wall surrounding the atomizing means, in the direction towards the outer wall of the air disperser, and the rest of said guide vanes are distributed on radii along the circumference of the pipe. The guide vanes are traditionally welded to a nearby part or parts of the air disperser.
Although this air disperser provides for reliable operation, the manner of manufacturing of the air disperser is relatively cumbersome and entails some disadvantages, as each guide vane must be welded in the exact position. In addition to the increased demand of manufacturing resources, the welding itself inevitably leads to slight deformations which in turn may lead to a reduced precision in the air flow. Furthermore, in certain fields of application, hygiene is a key factor and thorough cleaning of all parts of the air disperser is essential.